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MPhil thesis of Lo Chi Wa - Department of Electronic & Computer ...

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clkQBDclkclkclkFig. 56 Schematic diagram <strong>of</strong> the TSP D F/FControl logicBased on the combination <strong>of</strong> the inner status <strong>of</strong> the prescalar and the 4-bit modulusselect input, the control logic controls the multi-modulus and dual-modulus dividers toperform the required overall division ratio. Some combination logics are used todetermine the events for changing the modulus <strong>of</strong> the dividers by checking thecombination <strong>of</strong> the internal status and the modulus select input. The outputs <strong>of</strong> thecombination logics directly control the two dual-modulus dividers. Since the outputs <strong>of</strong>different phases have to be selected sequentially in order to have different modulus, adivide-by-4 divider is used to shift the output phase, as shown in Fig. 57. The divideby-4divider is implemented by four D-type latches as in Fig. 57. However, due to thepossible silent input to the divide-by-4 divider, static D-type latches as shown in Fig. 58have to be used.64

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